Process for the purification of metals and metallic alloys



Patented Mar. 9, 1937 UNITED STATES 2,073,019 A PROCESS FOR THE PURIFICATION or METALS AND METALLIC. ALLOYS 7 Henry Lepp, Cabourg, France, assignor of twothirds to Compagnie Gnrale dElectro-Metallurgie, Paris, France, and one-third to Socit dElectro-Chimie, dElectromtallurgie et des Aeieries Electriques dUgine No Drawing. Application November 2a, 1933, Serial No..700,113. In the Netherlands Novem- 'ber 28, 1932 It is known that the gases which dissolve in a bath of metals or metallic alloys in fusion generally have an adverse influence onthe mechanical properties of the metal obtained or of "the alloy formed. Hydrogen and sulphur dioxide are particularly harmful. Carbon monoxide and possibly also carbonic acid, nitrogen and cyanides are less harmful. I It hasalready been attempted to eliminate from 10 the molten bath these dissolved gases by treatment with an inert gas such as nitrogen and it has even-been proposed to treat the metal with gaseouschlorine. These treatments give, it is true, an improvement in the mechanical properties but the high cost and complication of the methods are obstacles to a general application.

The invention is based on the idea of producing a chemical combination of the gases and of displacing the equilibrium which is established at the temperature of the molten metal or of the metal alloy.

In accordance with the invention the gases dissolved in the metal such as H2, C0, C02, N2 and combinations of CN are eliminated by the addition of oxides of the metals which are found in the bath or of oxygen compounds adapted to form these oxides. v

' The molten metal (Me) has a reducing action on the moisture of the surrounding atmosphere in accordance with the following equation and it results that the hydrogen is absorbed by the molten metal. With the process in accordance with the invention" the hydrogen is eliminated by the addition of the metal oxides of the components of the alloy in consequence of the selective oxidation and displacement of the equilibrium. It should be pointed out here as a condition that the oxide in question added should never exceed the corresponding eutectic metallic metal-oxide. Thus for an alloy containing copper the addition of the cupric oxide should be located between 0% and 3.5%.

So far as the elimination of the other impurities is concerned, it should be pointed out that gases soluble in metallic baths can be considered as reacting on the metal or metals of the bath in accordance with the following equilibrium reactions:

3 Claims. (01. 15-92,

' The effect of the selective oxidation. is to displace completely the equilibrium of the above 10 reactions towards the left. Carbonic acidentirely liberated in the gaseous state is then insoluble and passes off into the atmosphere. Carbon monoxideliberated in the gaseous state may or may not be physically soluble; when it is soluble reinforced oxidation is resorted to inorder to transform it into CO2 which escapes into the atmosphere. Nitrogen liberated in the molecular gaseous state is always insoluble.

All the above reactions are exothermic when 20 considered" from right to left; they are moreover facilitated by the presence of the lessv .noble element and particularly so when the latter possesses a vapour tension.

Throughout this description and the claims, 25 the expression noble metal is frequently used. In the present case, this is meant to indicates. metal relatively unaffected by oxygen. Thus, less noble metal means a' metal more easily affected, more greedy of oxygen than another. metal to which it is compared.

Where the alloy' does not contain less noble metals than the principal element of the bath there is added moreover a less noble element (metal or metalloid) or'one of its compounds in such quantity that there remain at least traces of it in the casting obtained. This element presents preferably at the temperature of the bath a vapour tension greater than that of the more noble metal component. Such elements enter easily into reaction at high temperatures. By their own vapour tension they eliminate the gases dissolved and facilitate the selective oxidation indicated above. Thus for example according to the invention it is necessary to add to the bronzes y of tin before oxidation zincor phosphorus and" the oxidation should be conducted in such manner thatthere remain traces of zinc or phosphorus in the casting. Reduction usualy made is superfluous. o

such as is into sulphate which is very stable. I

When working in a neutral medium the quanti- In fact, the reduction of metallic oxides which may exist occurs, during the selective oxidation by the less noble elements in quantities suitably calculated, due to their greater affinity for oxygen than the metals of the oxides present.

Sulphur is eliminated through the medium of a double carbonate of barium and sodium. According to the chemical nature of the components of the alloy the operation is carried out in a reducing medium, a neutral medium, or an oxidizing medium. A reducing medium is obtained when wood charcoal is added for example. When the double carbonate only is added, a neutral medium is obtained unless by increase of the temperature it is transformed into a feeble oxidation. An oxidizing medium is obtained when an oxide is added, but a particularly intense reaction is obtained by the force of circumstances when a peroxide, preferably peroxide of barium,

-is added. In a reducing atmosphere the sulphur J is transformed into barium sulphide (BaS) BaS is formed because the heat of formation and 10-70 Ni and 90-30 Cu, the sulphur is partly in the form of elemental sulphur and partly in the form of S02. The latter are in equilibrium. When this alloy is treated in a reducing medium equilibrium is displaced and all the sulphur passes into the form of BaS.

An oxidizing medium is used with alloys containing for example tin or zinc, see above. In this case the sulphur passes into the form of sulphite (BaSOa). The latter is transformed by the addition of the above mentioned peroxide ties of sulphide and of sulphite formed depend on the temperature of the furnace. They are in equilibrium since in a reducing medium sulphide of barium is formed and in an oxidizing medium sulphite and finally sulphate of barium; therefore, in a neutral medium, equilibrium exists between the sulphide and sulphite of barium.

- With copper-nickel alloys it is necessary first to treat the bath by the addition of bariumsodium carbonate and carbon. Thereby the sulphur contained may be reduced from 0.5% to 0. If a reducing medium is not used all the sulphur cannot :be eliminated. Finally in order to eliminate the dissolved gases one should work in an oxidizing medium by addition of an oxide of copper or an oxide of nickel. In this case there can be added before oxidation as non noble components manganese, iron, zinc, cadmium, magnesium and anything which according to the periodic system can still enter into consideration.

Having now particularly described and ascertained the nature of my said invention and in what manner-the same is to be performed, I declare that what I claim is:

1. The process of purifying fused easily reducible metals and their alloys from impurities selected from the group consisting of sulphur.

sulphur dioxide, hydrogen, carbon monoxide, carbon dioxide, nitrogen, and cyanogen, which comprises flrst extracting the sulphur and sulphur dioxide by treatment in a furnace with a slag and carbon, said slag containing components which form in the furnace a fused double bariumsodium carbonate, thereafter skimming the bath,

I furnace fused double barium-sodium carbonate,

thereafter skimming the bath, then adding if not already present a less noble and relatively harmless element selected from the group consisting of zinc, phosphorus, cadmium, iron, magnesium,

and manganese, and thereafter adding predetermined quantities of an oxygen liberating substance selected from the group consisting of barium peroxide, and an oxide of at least one of the metals contained in the bath, the quantity of said oxide added being dependent upon the quantity or quantities of impurities present and at least sufiicient to effect the removal of said impurities, the quantity of said less noble element added being such that at least traces thereof willremain in the bath after thepurifying treatment has been completed.

3. The process of purifying fused easily reducible metals including copper, nickel'and their alloys from at least one of the impurities selected from the group consisting. of sulphur, sulphur dioxide, hydrogen, carbon,monoxide,'carbon dioxide, nitrogen, and cyanogen, which comprises first extracting the sulphur and sulphur dioxide by treatment with a slag and carbon, saidslag containing components which produce in the furnace fused double barium-sodium carbonate, thereafter skimming the bath, then adding if not already present a less noble and relatively harmless element selected from the group consisting of zinc, phosphorus, cadmium, iron,.magnesium, and manganese, and thereafteradding predetermined quantities or an oiwgen liberating substance selected from the group consisting of barium peroxide, and an oxide of at least one ofthe metals contained in the bath, the ;,quantity of said oxide added being dependent upon the quantity or uantities of impurities present, and at least sufcient to effect the removal of said impurities, the quantity of said less noble element added being such that at least traces thereof will remain in the bath after the purifying process has been completed.

HENRY LEPP. 

